Apparatus for coating tablets

Abstract

A non-fluidized bed apparatus for coating tablets has a base plate of which a portion of the upper surface is inclined towards an upward directed two-fluid or three-fluid nozzle. Ducts through the base plate around the nozzle produce jets of process gas in a direction intersecting an imaginary centre line of the spray produced by the nozzle. Atomizing gas from the nozzle is muffled shortly after it has left the nozzle to decrease the upward scattering effect of said gas on the tablets being coated. No partition is used for separating upward and downward flow of tablets during the coating process. In the coating process the amount of atomizing gas supplied to the nozzle is limited to reduce the tablet scattering effect of said gas.

What is claimed is:  
     
       1. An apparatus for coating tablets comprising: 
       a housing including at least one coating station which comprises:  
       a perforated base plate having an inclined upper surface;  
       an upward directed two-fluid nozzle located centrally in the base plate, said inclined upper surface being inclined toward the nozzle;  
       means for providing coating liquid to said nozzle to provide a spray from said nozzle;  
       means for providing gas to the nozzle to provide a flow of atomizing gas from said nozzle;  
       means for providing an upward gas stream through the perforations in the base plate; and  
       muffling means for pneumatically muffling the atomizing gas shortly after the atomizing gas has left the nozzle to decrease upward scattering effect of said gas on the tablets being coated,  
       wherein the perforations of the base plate are ducts arranged around the nozzle such that their respective longitudinal axes intersect at a center line of said nozzle and  
       wherein an area above the base plate influenced by the spray and the atomizing gas flow from said nozzle, and by gas flow from the muffling means and from the ducts, is without partition.  
     
     
       2. An apparatus according to claim  1 , wherein the means for pneumatically muffling the atomizing gas comprises outlets of gas supply means encircling the two-fluid nozzle and providing a rotating upward gas flow which meets the upward spreading atomizing gas stream from the two-fluid nozzle to decrease the upward velocity thereof and to deflect said upward gas flow into a broader swirling flow. 
     
     
       3. An apparatus according to claim  2 , wherein said gas supply means are grooves in the base plate connected to a plenum which also supplies gas to said ducts in the base plate. 
     
     
       4. An apparatus according to claim  2 , wherein said gas supply outlets debouch in an annular upward open cavity encircling the nozzle. 
     
     
       5. An apparatus according to claim  1 , wherein the means for pneumatically muffling of the atomizing gas comprises a mantel surrounding the two-fluid nozzle thereby forming a three-fluid nozzle. 
     
     
       6. An apparatus according to claim  1 , wherein the inclination of the base plate to the horizontal level is 5-20°, preferably 10-15°, and the ducts concentric around the nozzle are essentially perpendicular to the inclining upper surface of the base plate. 
     
     
       7. An apparatus according to claim  6 , wherein the distances between the ducts are selected depending on the size of tablets to be coated to be from 0.2 to 1.5 times the largest dimension of the tablets. 
     
     
       8. An apparatus according to claim  1 , wherein a vertical or a slightly upward broadening conical wall extends from the periphery of the inclined area of the upper surfaces of the base plate, which wall at distance from the base plate changes direction to form a more expanding conus. 
     
     
       9. An apparatus according to claim  1 , wherein said housing includes a plurality of said coating stations mutually separated by partial separating walls placed on or close to the base plates, the height of which walls is less than the maximum height to which the tablets are lifted during the operation of the apparatus, thereby enabling controlled transfer of tablets from one station to another.